1. Technical Field
The embodiments herein generally relate to complementary metal oxide semiconductor integrated circuit (CMOS IC) technologies, and, more particularly, to power management systems used in CMOS IC technologies.
2. Description of the Related Art
In modern CMOS IC technologies, as MOS transistor oxide thickness scales down, the breakdown voltage becomes lower. The scaling breakdown voltage makes the circuit design challenging especially in portable applications such as cell phones where battery voltage does not scale down. Voltage regulators are used to regulate the battery voltage down to a level which is suitable for the CMOS technology used. DC-DC converters are typically used because of their good efficiency versus low dropout (LDO) regulators. In cell phone applications, the battery voltage is normally 3.6V. With a careful design, it is possible to implement an integrated CMOS DC-DC converter with 3.6V input in 0.13 um CMOS technology. However, when the battery is being charged, the voltage can increase to 4.2V and sometimes to 5.5V in pulse-mode chargers. Moreover, it is difficult to design the integrated CMOS DC-DC converter that operates from this high input voltage.
There are two alternative solutions that are currently being used. The first solution is to use a discrete DC-DC converter that is built using technology that tolerates high operating voltages. The size and cost of such a solution tends to be relatively high. The second solution is to use system-in-package (SIP) technology to reduce the size of the overall system. However, SIP solutions tend to have a large size, and high cost (due to packaging complexity in SIP), and low yield. The conventional synchronous design of a DC-DC converter is shown in FIG. 1. When the input is 0V, the NMOS switch is OFF and the PMOS switch is ON, then Vdg of the NMOS is at 3.6V which can easily destroy the device. Therefore, using a single NMOS and PMOS switch is not possible for the 3.6V level in this technology that has devices rated at much lower operating voltages. Accordingly, there remains a need for a converter capable of properly regulating battery voltage levels in a cellular telephone.